1. Field of the Invention
This invention relates to a developing agent for electrophotography to be used for forming a visualized image of an electrostatic latent image, and a developing method using the developing agent.
2. Description of the Related Art
There have been proposed a large number of electrophotography methods up to date. However, the electrophotography method is typically performed in the following procedures. Namely, first, an electrostatic latent image is reproduced on a photosensitive drum comprising a body of a photoconductive material. Then, a developing agent is electrostatically adhered to the photosensitive drum in conformity with the electrostatic latent image thereby developing the latent image, thus forming a developing agent image. The image thus formed with the developing agent is transferred to a transfer medium such as a sheet of paper, and finally fixed thereon by means of heat and pressure, or by using a solvent vapor.
In order to precisely visualize the latent image reproduced on a photosensitive drum, the toner particles constituting the developing agent are required to be sufficiently and uniformly electrified by way of friction. In a non-magnetic single-component developing process, the following measures are generally taken in order to uniformly electrifying individual toner particles. Namely, the formation of developing agent layer as well as the electrification of developing agent are controlled by pressing a layer-regulating blade down to a layer of the developing agent which has been retained on a developing roller.
In the developing process using a non-magnetic single-component developing agent, the chance of the toner particles being electrified is very limited due to the construction of its developing apparatus as compared with the developing process using a binary component developing agent comprising carrier particles and toner particles. Specifically, in the developing process using a non-magnetic single-component developing agent, the stage wherein the electrification can be most directly applied to the toner particles is the moment when the toner particles on the sleeve of the developing roller pass through the layer-regulating blade. Therefore, if the toner particles are not sufficiently rubbed at this moment of passing through the layer-regulating blade, an insufficient electrification of the toner particles will be resulted, thereby giving rise to the generation of fogging on photosensitive drum.
There has been proposed measures of lowering the flowability of toner in the non-magnetic single-component developing process in an attempt to reduce the fogging on a photosensitive drum. However, when the flowability of the toner is lowered, it gives rise to another problem of a blur in image in the latter half portion of the solid image.
As explained above, in spite of serious problem that will be brought about by the fogging on a photosensitive drum, there has been failed as yet to find a suitable means for reducing the fogging on a photosensitive drum without raising such a new problem.
U.S. Pat. No. 4,987,454 discloses that use is made of toner particles which have at most 12 .mu.m of 50% average particle diameter, at least 16 .mu.m particles in an amount of 10% or less, and a coefficient of variation {(standard deviation/50% average particle diameter).times.100% } in a value of 20% or less. However, the aforementioned problems have not yet been solved in a single-component development process.